Human skin has two broad tissue types, the epidermis and the dermis. The epidermis is a continually keratinizing stratified epithelium. The outermost layer of skin is the stratum corneum and functions as the primary barrier. The stratum corneum is the outermost layer of the epidermidis and varies in thickness as function of the skin location. For example in the hand palm this layer can reach a thickness of 300 micron while the thickness in the armpit is approximately 5 to 15 micron. The stratum corneum is 15-30 cell thick layer of non-viable corneocytes.
The electroporation of cells is a non-thermal technique in which electrical fields are used to create nano-scale defects in a cell's membrane, which may cause cell inactivity or death. Electroporation involves the application of brief electrical pulses that result in the creation of aqueous pathways within the lipid bi-layer membranes of biological cells. Electroporation depends on the local transmembrane voltage at each point on the cell membrane. It is generally accepted that for a given pulse duration and shape, a specific transmembrane voltage threshold exists for the manifestation of the electroporation phenomenon. This leads to the definition of an electric field magnitude threshold for electroporation (Eth). That is, only the cells within areas where E≥Eth are electroporated. If a second threshold (Eir) is reached or surpassed, electroporation will compromise the viability of the cells, i.e., irreversible electroporation will occur.
There are a number of existing technologies used to inactivate bacteria, including ultraviolet light, violet-blue light and photodynamic therapy. The use of cold plasma is also under investigation. The electroporation of bacteria is also known. The cell membrane structure of the bacteria and/or its biochemical pathways are disrupted by placing electrodes on a surface or in a liquid and by applying an appropriate voltage, thereby inducing inactivation of the bacteria. When the bacteria experiences a high electrical field pores are induced in the cell membranes of the bacteria and start to close again once the electrical field is discontinued. This process is called reversible electroporation. If the cells are exposed to an even higher electrical field, the induced pores become so large that after discontinuation of the field the pores do not close anymore and the cell dies. This process is called irreversible electroporation and is used to inactivate microorganisms or to kill tumour cells.
Whilst the inactivation of bacteria through electroporation in a laboratory setting is known. However, the use of electroporation for the purposes of directly treating skin to, for example, inactivate or kill the bacteria present on the surface of the skin is not known. Bacteria present on the surface of the skin may be involved in the generation of an unpleasant body odour by transforming components of sweat into malodorous volatiles. Not using electroporation for inactivating bacteria on the skin is primarily due to the difficulty of rendering the bacteria inactive in a safe manner whilst at the same time avoiding unwanted damage or irritation to living skin cells just below the interface between the stratum corneum and the next layer in the epidermis.
Another important issue is the need to ensure that no dangerous electrical currents are induced through the human body. In particular, nerves can be activated by electrical effects which could lead to pain sensation and/or involuntary muscle contraction. Whilst it is known to treat tumours within the human body using electroporation, the applied electroporation pulses have to be synchronized with the patient's heartbeat to prevent heart rhythm problems.
There is also a requirement to ensure that no excess heat is generated when carrying out the electroporation of skin. Sweat contains salt ions typically in the order of 4.5 g/L Sodium Chloride. Although with a relatively dry armpit, a high electrical field strength can be maintained relatively easily and with relatively low electrical current, a wet, sweaty armpit which constitutes a relatively low electrical resistance will inevitably result in a higher electrical current being generated to maintain the required electrical field strength.
A dermal electroporation device is known from WO2013066427A and primarily relates to the use of electroporation for the purpose of delivering drugs to dermal tissue. US2007060862A2 also discloses a transdermal delivery device in which the electrodes are used to control a current flow through the skin.